Providing Ethernet data services has becoming a trend for telecom operators. Because Ethernet technology is now characterized by low cost and high expansibility, it has evolved from a mainstream LAN technology to a primary data service access technology and is widely used in Metropolitan Area Network (MAN) by more and more telecom operators.
Ethernet data services can be classified into two types: Ethernet private line services and Virtual Local Area Network (VLAN) services.
Currently, however, most data transmission networks utilized by telecom operators are SDH/SONET networks. Therefore, it is naturally desirable for telecom operators and telecom equipment manufacturers to access and transfer Ethernet data frames effectively in a SDH/SONET network to meet the increasing demand for Ethernet data services. At present, several telecom equipment manufacturers have provided the devices to access and transfer Ethernet data frames in a SDH/SONET network. Those devices may be classified into 3 types according to their functional implementation:                (1) data mapping/demapping scheme;        (2) bridge scheme; and        (3) RPR scheme.        
Before discussing the prior art, for convenience, the following acronyms or abbreviations used throughout this specification and their description are provided: MPLS-Multi-protocol Label Switching; GFP—General Frame Positioning; VLAN—virtual Local Area Network; VMAN—virtual Metropolitan Area Network; and RPR—Resilient Packet Ring.
FIG. 1 shows a block diagram of device according to the data mapping/demapping scheme in a first prior art. The device comprises one or more user-network interfaces (UNI) 20 (standard Ethernet interfaces), one or more network—network interfaces (NNI) 30 (synchronous digital transmission channels), one or more mapping/demapping devices 101, 102, and so one. Each of the mapping/demapping devices corresponds to a unique UNI and a unique NNI. In use, the data frames entering the device via UNI 20 and data frames output from the device comply with Ethernet data standard, and data frames entering the device via a NNI 30 and data frame output from the device comply with synchronous digital transmission network standard.
The mapping/demapping device 10 maps Ethernet data frames entering the device via UNI 20 to become synchronous digital data frames, and outputs the mapped data frames via a NNI 30. Conversely, the mapping/demapping device 10 demaps the synchronous digital data entering the device via NNI to Ethernet data frames, and outputs the data frames via the UNI. However, the functionality of the prior art device is simple, thus it can only provide Ethernet private line services.
FIG. 2A shows a block diagram of the device utilizing bridge scheme in a second prior art. The device comprises one or more UNIs 20 (i.e., standard Ethernet interfaces), each of which corresponds to a unique bridge port. The device further comprises one or more NNIs 30 (i.e., synchronous digital transmission channels). The device further comprises a bridge device 400, which is described in detail in IEEE802.1 D and IEEE802.1 Q standards. The bridge device 400 comprises a plurality of bridge ports, each of which corresponds to a unique UNI or a unique mapping/demapping device. Each mapping/demapping device corresponds to a unique bridge port and a unique NNI. The data frames entering the device via UNI 20 and the data frames output from the device comply with Ethernet data standard, and data frames entering the device from NNI 30 and data frame output from the device comply with the standard of synchronous digital transmission network.
Data frames entering the device via UNI 20 enter the bridge device 400 via the bridge port corresponding to the UNI. The bridge device 400 calculates the bridge output port according to the address information in the data frames and sends the data frames to the corresponding mapping/demapping device 102 via the output port (i.e., the mapping/demapping device maps the data frames and then outputs them to the NNI), and vice versa.
In the bridge scheme, usually the operator is allowed to map partial or all UNIs to mapping/demapping devices in a one to one way through configuration. In this case, the device employs both of above technical schemes, so it is called an enhanced bridge scheme. The functional model of an enhanced bridge device is shown in FIG. 2B.
The disadvantages of the second prior art are:                (1) it is unable to provide integral VLAN service. If a plurality of subscribers are attached to the device via UNIs and there are conflicts among address spaces of Ethernet data frames of those subscribers, the device is unable to isolate the conflicts effectively, thus it is unable to provide services correctly to those subscribers;        (2) a common bridge (non-enhanced bridge) is unable to provide Ethernet private line service;        (3) a UNI can only support one service type (Ethernet private line service or VLAN service), which limits the access capability of the device. In some cases, although the processing capacity of the device is sufficient, new devices have to be added to improve access capacity because the UNIs have been used up; and        (4) a NNI can only support one service type (Ethernet private line service or VLAN service), which leads to low convergence capability of the device. In some cases, in a star topology network, although the processing capacity of the device is sufficient, new devices have to be added to improve convergence capacity because the NNIs have been used up. For telecom operators, this means not only new investment but also bandwidth waste.        
FIG. 3 shows a block diagram of the device utilizing RPR scheme in a third prior art. The device comprises one or more UNIs (e.g., standard Ethernet UNIs), two NNIs (i.e., synchronous digital transmission channels), and a RPR device 600, which is described in IEEE802.17 standard, two mapping/demapping devices, and a data processing device 500, which may be a data converging/deconverging device or a bridge device.
The data frames entering the device via the UNI 20 are processed as follows:                Step 1: the data processing device 500 processes the data frames (the data frames are converged if the data processing device is a data converging/deconverging device, and the data frames are switched if the data processing device is a bridge device);        Step 2: the data processing device 500 transfers the processed data frames to the RPR device 600;        Step 3: the RPR device 600 sends the data frames to the corresponding mapping/demapping device according to the address information in the data frames; and        Step 4: the mapping/demapping device maps performs mapping operation for the data frames and sends them to outside of the device via the corresponding NNI.        
Conversely, the data frames entering the device via the NNI are processed as follows:                Step 1: the mapping/demapping device performs demapping operation for the data frames and transfers the demapped data frames to the RPR device 600;        Step 2: the RPR device 600 processes the data frames and then sends them to the data processing device;        Step 3: the data processing device 500 processes the data frames (the data frames are deconverged if the data processing device is a data converging/deconverging device; the data frames are switched if the data processing device is a bridge device); and        Step 4: the data processing device 500 finds corresponding UNI according to the address information in the data frames and then outputs the data frames via the UNI.        
The disadvantages of this scheme are:                (1) it is unable to provide Ethernet private line service and VLAN service at the same time. If the data processing device is a bridge device, it doesn't support Ethernet private line service; if the data processing device is a data converging/deconverging device, it doesn't support VLAN service; and        (2) it can only be used in a ring topology network.        